Selectively activated electrochemical cell system

ABSTRACT

A power generating system is described including a plurality of electrochemical cells. The cells are generally arranged in sections that are selectively activated individually or in combination to produce power from selected cell sections. A method of generating power is also described. A first group of one or more electrochemical cells of an array of cells are selectively activated based on requirement of an associated load. The system switches to a second group of one or more electrochemical cells of the array when the first group is discharged.

RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. ProvisionalApplication Serial No. 60/306,769 entitled “Selectively ActivatedElectrochemical Cell System” filed on Jul. 20, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a selectively activatedelectrochemical cell system, and more particularly to such a systemwherein individual cells or groups of cells may be activated in varioussuccessions depending on energy and power requirements.

[0004] 2. Description of the Prior Art

[0005] A variety of systems use electrochemical cells such as batteriesand fuel cells to meet power needs. For example, many portable devices,backup systems, vehicles, and other power consuming systems useelectrochemical cells

[0006] A key requirement for an electrochemical cell system is to meetthe power requirements. Another concern relates to the energy of thecell, which is the length of time that the required power may beprovided to the load. Heretofore, it has been extremely difficult tocombine high power and high energy

[0007] A further problem associated with electrochemical cell systems,particularly primary batteries, is that once a battery is activated, itremains active until it is discharged by utilization of the usefulenergy in the battery, self discharge, corrosion, or combinationsthereof. Therefore, interruptibility of conventional batteries, in manycircumstances, is limited.

[0008] It would be desirable to provide a system that can produce highpower and high energy, while further allowing for interruptibility, andtherefore extending the useful lifetime of the system.

SUMMARY OF THE INVENTION

[0009] The above-discussed and other problems and deficiencies of theprior art are overcome or alleviated by the several methods andapparatus of the present invention, wherein a power generating system isdescribed including a plurality of electrochemical cells. The cells aregenerally arranged in sections that are selectively activatedindividually or in combination to produce power from selected cellsections. A method of generating power is also described. A first groupof one or more electrochemical cells of an array of cells areselectively activated based on requirement of an associated load. Thesystem switches to a second group of one or more electrochemical cellsof the array when the first group is discharged.

[0010] The above-discussed and other features and advantages of thepresent invention will be appreciated and understood by those skilled inthe art from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIGS. 1A-1C is a schematic depiction of one embodiment of aselectively activated electrochemical cell system in operation;

[0012]FIG. 2A is a schematic depiction of another embodiment of aselectively activated electrochemical cell system having activationswitches open;

[0013]FIG. 2B depicts the system of FIG. 2A in a mode of operationutilizing a section of a first type of cells;

[0014]FIG. 2C depicts the system of FIG. 2A in a mode of operationutilizing a section of a second type of cells;

[0015]FIG. 2D depicts the system of FIG. 2A in a mode of operationutilizing sections of both a first type and a second type of cells;

[0016]FIG. 2E depicts the system of FIG. 2A in a mode of operationshowing one section of a first type of cells partially discharged andfurther utilizing another section of a first type of cells;

[0017]FIG. 2F depicts the system of FIG. 2A in a mode of operationshowing one section of a first type of cells discharged and furtherutilizing another section of a first type of cells;

[0018]FIG. 3 is a schematic depiction of a selectively activatedelectrochemical cell system and associated subsystems;

[0019]FIGS. 2G & 2H graphically depict the condition and associatedoperational variations of the a selectively activated electrochemicalcell system and the system's response to a simulated load;

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

[0020] Referring now to FIGS. 1A-1C, a selectively activatedelectrochemical cell system 100 is schematically depicted in operation.The system 100 is selectively coupled to an electrical load 130. Thesystem 100 comprises a plurality of electrochemical cells 110-113arranged in a pair of strings (cells 110 and 111 in series, and cells112 and 113 in series). A controller 140 is provided to selectivelyactivate one or more of the strings. Note that the controller 140 maycomprise a computer operably coupled to switches associated with eachcell or a group of cells, a manually operated control coupled toswitches associated with each cell or a group of cells (which areswitched by a user as needed), or a combination thereof.

[0021] The type of battery may be primary or secondary (i.e.,rechargeable), or a combination of primary and secondary batteries. Thecells 110-113 may be the same or different. Types of batteries include,but are not limited to, alkaline, lead-acid, nickel cadmium, metal air,lithium polymer, nickel metal hydride, nickel zinc, magnesium zinc, anycombination comprising at least one of the foregoing, and the like. Oneor more of the cells may also be fuel cells, such as hydrogen based fuelcells such as proton exchange membrane fuel cells or solid oxide fuelcells, metal air fuel cells, any combination comprising at least one ofthe foregoing, and the like.

[0022] During operation, the power demands of load 130 are met by one orboth strings of cells 110, 111 or cells 112, 113. The number of thestrings selected is controlled by the controller 140. For example, ifthe power requirement for the load 130 is 100 W, and each of the cells110-113 are capable of producing 50 W, the controller 140 may activateonly the string of cells 110, 111 to power the load 130. If the powerdemand continues beyond the capacity of the selected cell string, thecontroller 140 may deactivate the cell string 110, 111 and activateanother fresh cell string (e.g., cells 112, 113).

[0023] By individually activating strings of cells, particularly inprimary battery systems, the limitations related to lack ofinterruptability are overcome. That is, by using one string of cells topower the load 130, the remaining string (or strings, as the system mayprovide) are left with the full power and capacity, and discharging ofsuch remaining cells is not initiated, even if the energy is providedfrom the string of cells 110, 111 to the load 130 is insufficient todischarge such string. Accordingly, if the system is interrupted, onlycells 110, 111 will be subject to detriments associated with dischargeinterruption (e.g., self discharge), unlike conventional battery systemsthat are not discrete and separately activatable.

[0024] In another example, if the load 130 requires 200 W for operation,the controller 140 may activate both the string of cells 110, 111 andthe string of cells 112, 113. As shown in FIGS. 1A-1C, the strings arein parallel, however, it is understood that they may be in series, orswitchable between series and parallel, depending on the loadrequirements.

[0025] In a further example, if the load 130 initially requires 100 Wfor operation, the controller 140 will activate the string of cells 110,111. If the demand subsequently rises to 200 W, the controller 140 willactivate the string of cells 112, 113 to power the load 130. Byappropriate control, the depth of discharge and the energy utilized fromeach cell can be maximized.

[0026] When one or more of the cells 110-113, or cell strings 110, 111and 112, 113, are discharged, they may be replaced (individually or instrings) by the user (e.g., manually) or with an automated system. Theone or more cells are preferably replaced without interruption of thepower output of the system (that is, if the load 130 is in continuingdemand for power from the system 100).

[0027] Referring particularly to FIG. 1A, both cell strings 110, 111 and112, 113 are inactive (note the switches are open and the cells are notshaded). To commence power to the load 130, where the single string ofcells 110, 111 is sufficient, the string of cells 110, 111 is activated,as shown in FIG. 1B (wherein the associated switch is closed, and cells110, 111 are shaded). In the event that additional power is required, orif cells 110, 111 are drained (e.g., below a predetermined voltagelevel), the string of cells 112, 113 may be activated, as shown in FIG.1C (wherein the switch for cells 110, 111 may remain closed, or beopened (as indicated by dashed lines), and wherein drained cells areindicated with diagonal stripes). Note that the cells 110, 111 mayremain in parallel to drain any remaining power therefrom.

[0028] The controller 140 may be a computer that is operably coupled toswitches to selectively activate one or more of the strings of cells110, 111 or 112, 113. The controller 140 may monitor the needs of theload 130 to selectively activate one or more of the strings of cells110, 111 or 112, 113. Alternatively, the system 100 including acomputer-based controller 140 may be manually operated. The controller140 can monitor the load requirement, such that a determination is madeas to how many of the strings of cells 110, 111 or 112, 113 to activate,and in what configuration (i.e., parallel, series, or a combinationthereof), if applicable. Switching between the cells may be based on atimer, such that once activation commences, the controller 140 willswitch to another cell after a certain period of time. The time may be aconstant for the particular cell or type of cell, or may vary based onmonitoring of the load 130. Alternatively, the switching may be based onthe status of the selectively activated string(s), which can bemonitored by the controller 140. The status may be monitored by varioussub-systems, including but not limited to: monitoring the real-timepower output of the selectively activated cell(s), wherein the cell(s)will be switched when the remaining calculated energy or the voltagedrops below a preselected level; or monitoring the chemicalcharacteristics the cell(s) (e.g., by monitoring the expansion of thecell, which (in metal air cells) may be related to the chemicalproperties since the metal is converted to a higher volume metal oxidematerial; or by monitoring the composition of the electrolyte).

[0029] The controller 140 may also provide other features, including,but not limited to: monitoring the status of the cells includingnon-active cells (individually or in groups), monitoring the temperatureof the system 100; providing cooling when needed (wherein a coolingsub-system is also provided in the system 100); automatically ejectingstructures containing one or more of the cells when discharged tofacilitate replacement thereof (wherein an ejection sub-system is alsoprovided in the system 100); providing safety features, such asindicators, self-deactivation, and self-extinguishing (e.g., in theevent of fire, wherein an extinguishing sub-system is also provided inthe system 100); or any combination comprising at least one of theforegoing. The power output of the system 100 may also be conditioned orconverted, for example, from DC to AC, or from DC to DC (at differentvoltages), as is known in the power supply art. The system and/or loadsmay also be protected with one or more circuit breakers or fuses.

[0030] Power for the controller 140 and any included sub-systems may bederived from one of the cells in the system 100. Where a rechargeablecell is provided, it is preferred to power the controller with saidrechargeable cell. Alternatively, a suitable capacity rechargeable cellcan be provided that is dedicated to the controller.

[0031] In another embodiment, a system may be provided wherein each cellis activated by incorporation of electrolyte in the cell. Whenelectrolyte is added from a separate source, such as a bladder, syringe,tank, etc., the cell is activated. Thus, virtually infinite shelf lifemay be attained for the inactivated cells. For example, a systemmaintaining electrolyte out of contact with active cell components isdescribed in U.S. Provisional Application Serial No. 60/309,730 entitled“Reserve Battery” filed on Aug. 2, 2001 by Nicholas Pasquale.

[0032] Referring now to FIGS. 2A-2H, another embodiment of a selectivelyactivated electrochemical cell system and various modes of operationthereof are depicted. A selectively activated electrochemical cellsystem 200 includes a plurality of cell strings 210, 212, 214, 216 and218. Note that any number of strings, or cells within each string, maybe incorporated in the system, depending on the particular needs.

[0033] In the system 200, string 218 is a string of relatively highpower producing cells with relatively low energy capacity (as comparedto strings 210, 212, 214 and 216), and strings 210, 212, 214 and 216 arestrings of relatively high energy capacity cells with relatively lowpower output (as compared to string 218). For example, string 218 maycomprise a string of secondary batteries (e.g., rechargeable lead-acidor nickel cadmium), and the strings 210, 212, 214 and 216 may compriseprimary batteries (e.g., alkaline cells or metal air cells). Thissystem, a hybrid system, is particularly useful for meeting demands ofload 230 when the power requirement increases, as in a spike, induction,inrush, start-up, or other transient load characteristic.

[0034] For example, consider an environment wherein the system 200 isutilized as a backup power system, and that the load 230 typicallyoperates at less than 100 W, and occasionally increases to 300 W.Further, consider the example where string 218 comprises a high power(300 W), low energy (50 W-H) lead-acid battery, and strings 210, 212,214 and 216 comprise high energy (500 W-H), low power (100 W) zinc-airbatteries, that may be replaced or refueled (e.g., by replacing the zincin the batteries). String 218 is intended to handle up to 300 W peaks ofthe load 230. Strings 210, 212, 214 and 216 may be used for lower powerrequirements. In one example, string 218 may be connected to the load230 via a diode that only becomes forward biased when the current demandof the load 230 is sufficient to cause a voltage drop within one of theselected strings 210, 212, 214 and 216 corresponding to a 100 W load(e.g., the maximum of each of each of strings 210, 212, 214 and 216).Further, for low power uses, the string 218 may handle the load 230 forthe first few minutes of operation of system 200, or when it is knownthat the system 200 will be operational for only a few minutes. In thismanner, one or more of the strings 210, 212, 214 and 216 are notactivated until string 218 is discharged. With certain types of cells,once a cell is activated, it will remain active until it is dischargedeither by extracting the useful energy or by self-discharge. Therefore,by activating only certain strings, the power reserve (i.e., within theinactivated strings) remains intact.

[0035] In the mode of operation depicted in FIG. 2B, the switchassociated with string 210 is closed, thus string 210 is providing powerto load 230. As discussed above, this situation is intended for loaddemands below the maximum power of the string 210. Further, use of thestring 210 is preferably for a time period sufficient to utilizecapacity with the string 210, so as to minimize wasted power(particularly wherein the nature of the cells within the string 210 aresuch that self discharge is a concern).

[0036] In the mode of operation depicted in FIG. 2C, the switchassociated with string 218 is closed, thus string 218 is providing powerto load 230. As discussed above, this situation is intended for loaddemands above the maximum power capabilities of the string 210. Thestring 218 is preferably activated below a time period that wouldotherwise completely drain the cells therein. Thus, in various preferredembodiments, the control approximates the upcoming needs of the system200, and causes utilization of string 218 for, e.g., transients or shortterm needs.

[0037] In the mode of operation depicted in FIG. 2D, the switchesassociated with string 218 and string 210 are closed. In one embodiment,depending on associated control (not shown), string 218 may providepower to load 230, whereas string 210 provides recharging current forstring 218. In another embodiment, string 210 may provide power to bothmeet the needs of load 230 and recharge string 218. In still a furtherembodiment, strings 210 and 218, in parallel, may provide power for theload 230, e.g., during a high current transient condition.

[0038] In the mode of operation depicted in FIG. 2E, the switchesassociated with strings 210 and 212 are closed. In this embodiment, asdepicted by the shading variations in the Figure, string 210 has been inoperation for some time when string 212 is initiated. For instance, thismay be useful when the current demand for the load 230 increases to ahigher level for a period of time, and the capacity of the string 218 isinsufficient. Further, this mode may be useful to compensate for anyvoltage drop in the string 210 after a period of operation.

[0039] In the mode of operation depicted in FIG. 2F, the switchassociated with string 212 is closed. In this embodiment, as depicted bythe diagonal lines in the cells of string 210, string 210 is dischargedor substantially discharged. Note that the switch associated with string210 may be closed or open (as indicated with dashed lines). In certaincircumstances, it may be desirable to maintain connection with string210, for example, to withdraw any remaining power from the cells.

[0040] Graphical simulated operational analysis of a hybrid systemsimilar to that depicted in FIG. 2A is provided in FIGS. 2G and 2H. Inparticular, the system is simulated based on a section of zinc-airbatteries (Zn-air) and a section of lead acid (Pb—Ac) batteries. Thesection of Zn-air cells is characterized as two parallel strings of tencells. Each cell has an open circuit voltage of 1.44 V, an internalresistance of 75 milliohms, a capacity of 15 W*h, and a depth ofdischarge of 50%. The Pb—Ac section is characterized by six BolderTechnologies 95 Sub C (Golden, Colo.) cells in series each having anopen voltage of 2.00 V, 4.4 milliohms internal resistance, an energycapacity of 0.862 A*h per cell at 50 A, and a recharge efficiency of55%. The Pb—Ac section engages at about 8 amperes of current draw,generally to supply the difference between the upper load demand and theZn-air power output. The simulation is based on a theoretical, but quiteplausible loading profile.

[0041] As shown in FIG. 2G, as the load current increases, the Zn-airsection is unable to meet the demands, causing a voltage drop. Tocompensate, the Pb—Ac supplies additional power. As shown, this occurswhen the load is about 8 amperes, corresponding to 11.4 volts. At thislevel, a diode associated with the Pb—Ac section becomes forward biased.

[0042] Referring to FIG. 2H, a simulated 120 second load condition isdepicted. Note that while the load current is low (e.g., lower thanabout 5 A), the load is powered by the Zn-air section. However, as theload spikes to about 30 A, the draw on the Zn-air section increases (toa maximum of 9.4 A), while the draw on the Pb—Ac section increases from0 A to over 20 A. As the load current decreases, the draw from the Pb—Acsection is halted, and accordingly, the Zn-air section powers the load.Further, the Zn-air section provides recharging power to the Pb—Acsection. A similar effect is shown with the load current spike to about15 A. Note that the recharging allows the Pb—Ac section to be completelyrecharged at the end of the 120 second cycle.

[0043] Referring now to FIG. 3, a selectively activated electrochemicalcell system 300 is depicted, including associated subsystems which maybe present in a hybrid system for enhanced control and capability. Thesystem 300 includes primary electrochemical cell sections 310 (cells 310₁, 310 ₂, 310 ₃, 310 ₄ . . . 310 _(N)), 312 (cells 312 ₁, 312 ₂, 312 ₃,312 ₄ . . . 312 _(N)), and 314 (cells 314 ₁, 314 ₂, 314 ₃, 314 ₄ . . .314 _(N)), wherein the sections are in parallel; and a secondaryelectrochemical cell section 318 (cells 318 ₁, 318 ₂, 318 ₃, 318 ₄ . . .318 _(N)), which is in parallel with the primary cell sections 310, 312and 314.

[0044] In general, the cell sections are controlled with a controller340, which performs various functions and interacts with associatedsubsystems. For user interaction with the system 300, a user panel 342is provided, including user control and status display. Sectionalactivation is provided with a power switch drive signal for controllingthe switches associated with the sections. The AC line, e.g., which thesystem 300 backs up, is monitored by the controller 340. Current andvoltage sensing systems are also provided, for example, to provide datafor use by the controller 340. In systems where each cell undergoes amechanical or electronic activation (i.e., as opposed to sectionalactivation), an actuation/triggering control signal may be provided.Also, in certain types of cell systems, temperature sensing is alsoprovided, for example, whereby the controller 340 provides signals tooptional fans 354 (as indicated by dashed lines) Note that while severaltypes are displayed in FIG. 3, it will be apparent to those skilled inthe art that certain functions are not required in certain types ofcells or necessary systems, and further that additional functions mayalso be provided.

[0045] To provide for a hybrid system 300, wherein the secondary section318 undertakes power provision during certain circumstances, a diode 346is provided. The diode 346 only becomes forward biased when the currentdemand of the load is sufficient to cause a voltage drop within one ofthe selected strings 310, 312 and 314. With a sufficiently intelligentcontroller 340 combined with sufficient sensing elements the diode 346can be eliminated (as well as its associated power losses) since theswitch in series with string 318 can be controlled in a manor thatreplaces the function of the diode 346.

[0046] The system 300 further includes various associated subsystems.Power supplies 344 are included for providing suitable power forcontroller 340, and any included drivers, transducers, actuators, etc. Amain charger 348 is also included, which provides suitable powerconditioning (e.g., DC to DC) to allow charging of the secondary cellsection 318 (e.g., a Pb-acid system) from the primary cell sections 310,312 and 314 (e.g., Zn-air). Also, an optional DC-AC inverter 350(indicated by dashed lines) may be provided, for example, to invertpower from the electrochemical cell system 300 to a AC load or loadsystem. Further, an optional accessory charger 352 is provided(indicated by dashed lines), e.g., which inverts an AC line to suitableDC power for charging the secondary cell section 318. Of course, pluraloptional circuit breakers 356 (indicated by dashed lines) may also beincluded, generally to protect the system circuitry and any connectedloads.

[0047] The selectively activated electrochemical cell system providesmany benefits in various applications. For example, emergency powersystems may endure very long periods of non-operation withoutsubstantially diminishing power or capacity, even after they have beenoperated. Electric vehicles may be able to provide the necessary powerfor short term boosts, for example, with a rechargeable cell, whileoperating under “normal” conditions with a plurality of selectivelyactivated primary cells, thereby facilitating long trips without manualrefueling of the cells or recharging. Uninterruptible power supplies mayinclude, for example, several arrays of typical primary or secondarybatteries, such as “AA” size batteries. When one array is consumed, thecontroller switches to another array, whereby the user may replace theconsumed array without power interruption.

[0048] While preferred embodiments have been shown and described,various modifications and substitutions may be made thereto withoutdeparting from the spirit and scope of the invention. Accordingly, it isto be understood that the present invention has been described by way ofillustrations and not limitation.

1. A power generating system comprising: a plurality of electrochemicalcells that are selectively activated individually or in combination toproduce power from selected cells.
 2. The power generating system as inclaim 1, further comprising a controller to selectively activate one ormore cells.
 3. The power generating system as in claim 1, wherein one ormore of the cells comprise primary batteries and one or more of thecells comprise secondary batteries.
 4. An electrochemical power systemfor connection to a load comprising: a plurality of arrays ofelectrochemical cells in a parallel configuration, each array includinga plurality of electrochemical cells arranged in series; and acontroller system for controlling which one or more arrays of theplurality of arrays is to be in connection with the load.
 5. The systemas in claim 4, wherein the controller system includes a switchassociated with each of the arrays and a logic system.
 6. Anelectrochemical cell system comprising: a plurality of sections ofelectrochemical cells, wherein individual sections are controlled foractivation of one section or for activation in successions.
 7. Theelectrochemical cell system as in claim 6, wherein at least one sectioncomprises metal air electrochemical cells.
 8. The electrochemical cellsystem as in claim 7, further wherein at least one section comprisessecondary electrochemical cells.
 9. The electrochemical cell system asin claim 8, wherein the secondary electrochemical cells have a higherpower output and lower capacity than the metal air electrochemicalcells, and further wherein activation control provided for activation ofthe metal air electrochemical cells at a load below a predeterminedlevel value or range and activation of the secondary electrochemicalcells at a load above a predetermined level value or range.
 10. Theelectrochemical cell system as in claim 8, wherein upon activation ofsection of metal air electrochemical cells in response to a loadcurrent, the activated section discharges to a preselected depth ofdischarge or until completely discharged.
 11. The electrochemical cellsystem as in claim 7, wherein the metal air electrochemical cellscomprise reserve cells wherein cell components selected from the groupof electrolyte, oxidant, anode, cathode, and any combination comprisingat least one of the foregoing components are incorporated into the cellsupon activation or at a controlled time prior to activation.
 12. Amethod of generating power comprising: selectively activating a firstgroup of one or more electrochemical cells of an array of cells based onrequirement of an associated load; and switching to a second group ofone or more electrochemical cells of the array when the first group isdischarged.
 13. The method as in claim 12, further comprising switchingto a third group of one or more electrochemical cells of the array whenthe second group is discharged.
 14. The method as in claim 12, whereinthe first group comprises rechargeable cells and the second groupcomprises primary cells.